Datatemplate for Tabitem doesn't cover all the tabitem space (WPF Tabcontrol)

Question

i have a datatemplate for a tabitem in a tab control. The datatemplate doesn't cover all the Tabitem control, the beckground is a gray or white, control default color.

The Datatemplate of the TabItem:

<DataTemplate x:Key="ClosableTabItemTemplate">
            <Border BorderThickness="1" BorderBrush="Transparent" CornerRadius="4">
                <!--Border to make the tab item gap from the content-->
                <Border x:Name="InsideBorder" BorderThickness="3" BorderBrush="#D6EAFF" CornerRadius="4">
                    <!--Border for the rounded corners-->
                    <!--TabItem Content Grid-->
                    <Grid x:Name="tabItemGrid" ShowGridLines="True" Margin="0" Background="#D6EAFF">
                        <Grid.RowDefinitions>
                            <RowDefinition Height="Auto"/>
                        </Grid.RowDefinitions>
                        <Grid.ColumnDefinitions>
                            <ColumnDefinition Width="25"/>
                            <!--Icon Column-->
                            <ColumnDefinition Width="1*"/>
                            <!--Title Column-->
                            <ColumnDefinition Width="20"/>
                            <!--Close Button Column-->
                        </Grid.ColumnDefinitions>

                        <!--Icon of tab Item-->
                        <Image Grid.Column="0" Grid.Row="1" Height="18" HorizontalAlignment="Left" Source="Images/tab1.jpg"/>

                        <!--Title of tab Item-->
                        <Label Name="TabText" Grid.Column="1" Grid.Row="1" Content="TabItem"  Height="23"  HorizontalAlignment="Left" 
                                           Margin="4,1,0,0"  VerticalAlignment="Top" FontFamily="Courier" FontSize="12" />

                        <!--Close button of tab Item-->
                        <Button Style="{DynamicResource TabButton}"
                                            Name="button_close" Content="x"
                                            Command="{Binding Path=CloseCommand}"
                                            Grid.Column="2" Grid.Row="1" 
                                            Height="20" Width="20" 
                                            Margin="0,0,0,2" VerticalAlignment="Center" HorizontalAlignment="Right"
                                            FontFamily="Courier" FontStretch="Normal" FontWeight="Bold" FontSize="14" 
                                            Visibility="Visible" ToolTip="Close" 
                                            BorderBrush="Transparent" BorderThickness="0" Background="Transparent" Padding="0,0,0,0"
                                            >
                        </Button>
                    </Grid>
                </Border>
            </Border>



            <DataTemplate.Triggers>

                <DataTrigger Binding="{Binding RelativeSource={RelativeSource Mode=FindAncestor, AncestorType={x:Type TabItem}},Path=IsSelected}" Value="True">
                    <Setter TargetName="tabItemGrid" Property="Background" Value="#D6EAFF" />
                </DataTrigger>

                <DataTrigger Binding="{Binding RelativeSource={RelativeSource Mode=FindAncestor, AncestorType={x:Type TabItem}},Path=IsSelected}" Value="False">
                    <!--<Trigger Property="IsSelected"  Value="False">-->
                    <Setter TargetName="InsideBorder" Property="BorderBrush">
                        <Setter.Value>
                            <LinearGradientBrush EndPoint="0,1" StartPoint="0,0">
                                <GradientStop Color="#FFCCCCD0" />
                                <GradientStop Color="#FF526593" Offset="1" />
                            </LinearGradientBrush>
                        </Setter.Value>
                    </Setter>
                    <Setter TargetName="tabItemGrid" Property="Background">
                        <Setter.Value>
                            <LinearGradientBrush EndPoint="0,1" StartPoint="0,0">
                                <GradientStop Color="#FFCCCCD0" />
                                <GradientStop Color="#FF526593" Offset="1" />
                            </LinearGradientBrush>
                        </Setter.Value>
                    </Setter>
                </DataTrigger>
                <!--</Trigger>-->
            </DataTemplate.Triggers>
        </DataTemplate>

The Tabcontrol:

<TabControl Name="MainTabCtrl"  Margin="0" Padding="0" BorderThickness="0" Background="Transparent"
                        IsSynchronizedWithCurrentItem="True"
                        ItemsSource="{Binding Path=TabViewModels}" 
                        ItemTemplate="{StaticResource ClosableTabItemTemplate}">

when the Xaml code of the tabitem wasn't inside a DataTemplate it worked fine - the "Transparent" of the first border did the job and no gray/white background appeared. but when i moved the code inside a DataTemplate the gray background appeared.

How do i make the background of the tabitem transparent?

I added HorizontalContentAlignment="Stretch" VerticalContentAlignment="Stretch" to the tabcontrol, it only narrows the gray area a bit but it still exsits.

Answer 1

Try to set Padding for TabItems to zero.